1. Field of the Invention
The present invention relates in general to cylinder blocks of an internal combustion engine, and more particularly to the cylinder blocks of a so-called shallow bottom water jacket type wherein a bottom of a water jacket surrounding each cylinder is positioned above a lower deck portion of the cylinder block.
2. Description of the Related Art
Japanese Laid-open Patent Application (Tokkaihei) 6-299900 and Japanese Laid-open Patent Application 2000-291488 disclose cylinder blocks of the shallow bottom water jacket type, for an internal combustion engine. In these cylinder blocks, around each cylinder wall, there extends a jacket side wall to define therebetween a water jacket, so that under operation of the engine, cooling water is forced to flow in the water jacket to absorb heat of the cylinder wall. A lower end of the jacket side wall is connected to the cylinder wall through a jacket bottom wall. The jacket bottom wall is positioned above a lower deck portion of the cylinder block. As is known, the lower deck portion of the cylinder block is the portion from which a crank case extends downward.
With the shallow bottom water jacket, an upper part of the cylinder wall near the combustion chamber is effectively cooled by cooling water and due to absence of water jacket around the lower end of the cylinder wall, weight reduction of the cylinder block is possible accordingly. The above-mentioned published patent applications describe various advantages that are induced by such shallow bottom water jacket construction, which are for example, suppression of over cooling, improvement in fuel consumption, improvement in exhaust characteristics, improvement in heating characteristics of heating system, etc.,.